Slant 6 dies when driving

It hesitates and eventually will die, but will start right up and continue to hesitate. If it cools it will run smooth again for a while then if going from light to light the hesitation will begin again. It's a 74 with California emissions. Almost seems like a vacuum leak, but I don't see any broken lines.
My 76 Aspen /6 did a similar thing and turned out to be a massive vacuum leak in the vacuum advance unit